The present invention relates to a configuration for the spectral color division and/or recombination of light according to the preamble of claim 1.
U.S. Pat. No. 3,202,039 discloses a configuration for color division. It comprises a first prism with two first faces which form a first prism angle. On a second prism two faces form the second prism angle. One of the first and second faces each are disposed in parallel opposite one another. In this respect, the prism angles are positioned in alternating angular configuration. The opposing faces of the prisms are spaced apart by an air gap. The total reflections realized thereon lead from time to time to the targeted light division.
With respect to spectral color division and/or recombination operating according to a similar principle, reference can be made to U.S. Pat. Nos. 5,777,789 or 5,644,432. Baumeister, "Reflectors with Phase Compensation for a Reflective LC Colour Projection System", SID 98 DIGEST, pp. 679.
Realization of said air gap considerably raises the expenditures for the production of such systems. Added to this is the fact that through the total reflections a phase rotation between S- and P-polarization is induced which can only be controlled with difficulty. Without additional measures this phase rotation has a strong effect on the contrast of the light division. A further disadvantage is that light is misdirected to the air gap, due to the non-ideal interfacial surfaces, which often leads to a decrease of the image quality.
U.S. Pat. No. 5,748,365 discloses a so-called K prism in which, according to the graphic representation, prisms are disposed one on the other without an air gap. Thereby light-dividing faces are formed such that incident white light multiple reflection into a blue and a green channel, the red light is transmitted through the configuration.
It is the task of the present invention to propose a configuration of the type described in the introduction, which, on the one hand, retains the advantageous effect of a configuration as known, for example, from U.S. Pat. No. 3,202,039; and but, on the other hand, eliminates its disadvantages with respect to the image quality as well as also the production expenditures. This is attained when implementing the configuration according to the invention.
The present invention uses the following definitions:
Definitions
.cndot. Light, light with maximum energy in the spectral range 380 visible light: nm-720 nm .cndot. red light: light with maximum energy in the spectral range 580 nm-780 nm, in particular in the spectral range 600 nm-680 nm .cndot. green light: light with maximum energy in the spectral range 490 nm-605 nm, in particular in the spectral range 500 nm-600 nm .cndot. blue light: light with maximum energy in the spectral range 380 nm-510 nm, in particular in the spectral range 420 nm-500 nm .cndot. yellow light: light with maximum energy in the spectral range 560 nm-605 nm, in particular at 578 .+-. 3 nm .cndot. white light: light with red, blue and green light components transparent: negligible absorption in the spectral range 380 nm- 720 nm AdR: "Angle-dependent Reflection", spectral reflection behavior as a function of the angle of incidence of the reflected light AOI: Angle of incidence
Consequently, according to the invention the color division - with corresponding reflection--on the configuration according to the invention takes place by providing a thin film layer system between the prisms, which with respect to its AdR is matched to the prism angles. This permits, on the one hand, eliminating the disadvantages of the configuration prior known from U.S. Pat. No. 3,202,039 with respect to the air gap thereby that the opposing faces of the prisms can, according to the invention, oppose one another without an air gap. This permits the elimination of all of the disadvantages entailed in the described air gap regarding fabrication problems and image problems.
The light splitter configuration according to the invention compared with the division or recombination principle on so-called X-cubes, such as are known from the WO98/20383 by the same applicant, results on the configuration according to the invention in relatively small angles of incidence of the light on the thin film layer system essential for the color division and provided according to the invention. Therefrom follows further that, compared with the beam division or recombination on thin film layer systems of an X-cube, on the configuration according to the invention a very much smaller polarization shift of the light on its thin film layer system needs to be taken into consideration. In addition, the angle dependence of the light transmission and division becomes less pronounced which, in turn, has a positive effect on the fabrication tolerances to be maintained.
The possibility is given, furthermore, of better scattered light suppression on the light splitter according to the invention which increases the image quality and therein primarily the contrast.
This results in particular from the fact that the geometric conditions can be flexibly adapted on the configuration according to the invention.
Preferred embodiments of the invention are specified as is a system according to the invention in. In the following the invention will be explained by example with reference to the Figures.